Final answer:
To increase alertness, heighten mood, and decrease fatigue, coffee is commonly consumed due to the presence of caffeine, which acts as a neurotransmitter antagonist.
Step-by-step explanation:
To increase alertness, heighten mood, and decrease fatigue, coffee is commonly consumed. The stimulating effects of coffee are due to the presence of caffeine, which acts as a neurotransmitter antagonist and blocks the activity of adenosine, a neurotransmitter that promotes sleep. Consuming about 200 mg of caffeine, which is equivalent to about two cups of strong coffee or tea, can have these effects.